The present invention relates to a method and an installation for constructing a layer of armor strips around a tubular core of a flexible pipe for the transport of hydrocarbons.
The flexible pipes concerned are in this instance oil pipes of the unbonded type, as described in standards documents API17J and API RP 17B published by the American Petroleum Institute. These pipes usually comprise, from inside to outside, an inner carcass, an inner sealing sheath, a pressure vault, several plies of tensile armors and an external protective sheath.
The main function of the inner carcass is to absorb the radial crushing forces, for example those associated with hydrostatic pressure. It is made from a profiled metal strip and wound in order to clip together adjacent turns of said metal strip. The inner sealing sheath which covers it is most frequently extruded in plastic directly onto the carcass. The function of this sheath is to confine the fluid flowing in the pipe. As for the pressure vault, it is usually formed of a metal-form strip wound in adjacent turns about the inner sealing sheath. It therefore makes it possible to absorb the radial forces associated with the pressure of the fluid flowing in the pipe. The function of the tensile armor plies is to absorb the tensile forces which are applied to the pipe. These plies consist of armor strips wound helically with a long pitch around the pressure vault. The helix angles of these plies, expressed in absolute value, are less than 60° and more usually less than 55°. In order to balance the structure in torsion, the total number of tensile armor plies is usually even and the plies are criss-crossed.
These armor strips are usually of rectangular section and they therefore have two opposite faces that are substantially parallel with one another and respectively two lateral sides that are opposite to one another. The faces correspond to the two longer sides of the rectangle. The face called the inner face presses on the tubular core situated inside the armor ply concerned.
The difficulty lies in the application of a plurality of armor strips, in order to wind them together around the pressure vault which forms a tubular core with the inner layers that it comprises. And precisely, these armor strips have to be wound and adjusted relative to one another, side to side, so that their inner face presses stably on the tubular core, with the minimum possible residual stresses, in order to prevent a subsequent deformation of the armor ply and a swelling of this ply in particular conditions of use of the flexible pipe.